Last week I was at NAB for the first time and to be honest I never knew the show had gotten that big. Every hall was full. I happened to be in the hall that had a lot of post-production and video equipment, as well as screens and media servers, etc.
One of my colleagues at Chief told me that I needed to go and check out this direct view LED array down the hall a little way. I grabbed my brother-in-law David who was in town for the show from Lockheed Martin and off we went. As we approached the screen we weren’t overly impressed honestly and I started mentally cursing my Chief counterpart for wasting our time with this large 2mm dot pitch screen.
Just then however David pointed across the aisle and there it was. A SiliconCore 1.5 mm dot pitch LED array that must have been 10 feet tall and 18 feet wide displaying some awesome 4k time-lapse photography as well as some computer animation. At 10 feet it was stunning, despite some small glare issues due to the glossy substrate used to surround the LEDs (they are changing it to matte shortly they said, so that should mitigate this issue). At 4 feet it was still amazing, and I started thinking that LED may be getting good enough now to replace some video wall and projections systems I’ve seen applications for.
That was until we found out the cost. The 1.5 mm was related at being around $55,000 per square meter, or to put it in more relative terms, the equivalent of a 43″ diagonal screen would be about $33,000.
Given that, video walls and front projection systems will most likely be around for quite some time. How do you choose what technology is going to give you the best bang for the buck?
I wanted to do a quick comparison of three methods of creating large format video experiences: Projection, Video Walls, and LED arrays. Besides the obvious concern of budget, are there reasons that you would use one over another? I have some suggestions, but first let’s look at a few other differences.
I first want to qualify the term “large format” though as over 100″ in diagonal. In the following examples, I am using a screen size of approximately 165″-175″ diagonal just to illustrate some of the points with real data. Given that, the examples below compare a 165″ projection system with a 25,000 lumen 4k projector (like the Christie Mirage 4k25), a 165″ diagonal video wall (a 3×3 wall with nine 55″ diagonal,1080p screens), and a 175″ diagonal SiliconCore 1.5mm LED array (an 8×8 LED cabinet array ).
One of the major differences in the systems above will be total pixel density. To figure that out, you need to divide the number of total pixels by the total square inches of the screens.
The projection system is the easiest, as the projector yields 4096×2160 resolution or 8,847,360 total pixels spread over 11,664 sq inches (a 165″ screen is 144″ x 81″ wide) for a density of 758 pixels per square inch.
The video wall yields 1920×1080 resolution times 9 monitors for a total of 18,662,400 pixels spread over that same 11,664 inches for a density of 1600 pixels per square inch.
The LED array actually lists pixel density in its specification as it is fixed based on the LED elements in each cabinet. It is listed as 443,999 pixels per square meter. A quick conversion brings that figure to 286 pixels per square inch.
Another major difference in the systems above will be brightness. Since both video wall displays and LED arrays are rated in “nits”, I will stick with that method to minimize conversions.
The projection system is this case is the hardest as we need to calculate it. The projector yields 25,000 lumens of brightness spread over 81 sq feet yields 308 lumens per foot or 1055 nits if we use a unity gain (1.0) screen.
The LED array lists its brightness at 2000 nits at max after calibration, (get some sunglasses for this one!)
The other half of brightness is contrast. It’s nice to have a bright image, but if you can’t achieve any perceived black level, you just get a washed out mess.
We really have to make some assumptions to start to speculate contrast level on a projections system. Ambient light plays a huge role in that figure, as even though the projector has a contrast ratio of 2000:1, ambient light on the screen will reduce that greatly (in fact even commercial theaters only aim for between 100:1 at the bare minimum and 500:1 as an ideal value.) So even if I use an optimistic 5 ft candles of ambient light on the screen (about the same as a bright media room or dim boardroom), our contrast ratio is at 60:1.
Again the video wall displays can vary, so I’ll use the same Samsung UD55D model as above. Contrast is 3500:1. (Beware of claims of “infinite contrast” as it is technically impossible to achieve and is more a marketing gimmick than anything else).
The SiliconCore LED technology doesn’t denote contrast ratios in its literature, but based on similar LED technology on the market at the same 2000 nit brightness, it is most likely around 4000:1.
So, I mentioned earlier this would be a huge determining factor in the design of any system as well. For that reason I have to give some estimated retail costs here. The pricing really doesn’t include anything other than the screens. The content delivery system or special scalers etc would be in addition to these costs.
The projection system’s Christie Mirage 4k25 projector is in the range of $100,000 retail. Add a nice 165″ screen to reflect those 25,000 lumens back to the eyes and you have about $105,000.
The video wall displays again vary, so I’ll use those Samsung UD55D models. MSRP is around $8,600 per panel and you have 9, bringing this screen to around $77,400.
Finally the SiliconCore system was quoted to us on the NAB floor at approximately $55,000 per square meter. A 175″ diagonal, 16:9 screen is 153 inches wide by 86 inches tall yielding 13,158 sq inches. Some American to Brit conversion gets us about 8.5 square meters of screen area bringing the LED array in at $467,500.
A quick note:
The specs on the above systems vary widely and one feature set may drive the technology choice.
Lets say native 4k resolution is needed and no scaling is desired. In that case the projections system already fits the bill at $105,000. A 2×2 screen wall with four 80″, 1920×1080 Sharp professional displays would also net 4k resolution (although with larger bezels but I use those to get the 160″ diagonal) and an MSRP of $50,380. The only way to get true 4k on SiliconCore’s 1.5 LED system is to add more modules which adds more size as well. To get the 8.25 million pixels in consumer 4k (3840 x 2160) you would need 144 cabinets, netting a screen diagonal of 260 inches and a cost of “1 million dollars!”
Application, Application, Application.
At the end of the day we know that only the application can really determine which system is “best”. Given the data above however some general guidelines can be drawn.
Applications like engineering or visualization where the accuracy of the image is extremely important and where viewing distances may be extremely short and done in well-lit rooms would benefit from the higher pixel density and contrast of a video wall. If you need more pixel density, you decrease the size of the displays and use more of them. Going from a 3×3 video wall with 55′ displays to a 4×4 video wall with 46″ displays only increases the diagonal by 19″ to 184″, but increases the pixel density from 1600 pixels per square inch to 2304 pixels per square inch. The bezels will create some break-up of the image on whole, but will be acceptable to achieve the accuracy.
Immersive applications like theater, 3D, or simulation installed in rooms where light is controllable, would most likely be best suited by the projection based systems. They yield great pixel density (which can actually be increased by blending multiple projectors into one image) and the absence of bezels means that they will submerse the viewer deeper into content without distraction.
Digital signage systems where viewing distances are greater and ambient light is high could be well suited by both the video wall and LED arrays, as the increased viewing distance compensates both for the bezel interruptions and pixel density issues in the screens respectively.
Currently, the SiliconCore 1.5mm LED array discussed is an indoor unit, (I’m sure 1.5mm outdoor units will follow), but in outdoor applications, or applications in store windows even where direct sunlight can reflect off of glass and greatly affect the image, the high brightness of the LED arrays is key and would make it the clear choice.
The great thing is that today we have options. Now those options may be limited by budgets as they most times are, but knowing where to start based on an application and then discussing the alternative technologies and the resulting compromises can really do a lot to make sure the end result is a system that delivers the best bang for the buck.
There is a lot to consider sure, but the initial groundwork up front always yields a better end result.